Electrostatic printing system and method using a moving shutter area for selective mechanical and electrical control of charged particles

ABSTRACT

An electrostatic printing system and method in which a charged particle stream directed toward a print receiving medium is selectively controlled by mechanical and electrical modulation or shuttering and mechanical motion of the shutter area to achieve character serial and line serial printing.

United States Patent [.191

Tisch et al.

I 1 ELECTROSTATIC PRINTING SYSTEM AND METHOD USING A MOVING SHUTTER AREAFOR SELECTIVE MECHANICAL AND ELECTRICAL CONTROL OF CHARGED PARTICLES[75] Inventors: Thomas A. Tisch, Saratoga; Thomas A. Jenkins, Redwood.both of Calif.

" Assigneer ,Ele i t 29- ,Ce qt nqt if- [22 Filed: July 19, 1972 [21]Appl. N0.: 273,239

[52] US. Cl. 346/74 EB, 346/74 ES [51] Int. Cl. G0ld 15/06 [58] Field ofSearch 346/74 ES, 74 EB, 75;

[56] References Cited UNITED STATES PATENTS Czipps 346/74 ES 11]3,815,145 1 5] June 4, 1974 3,362,325 1/1968 Foster 346/74 ES 3,599,22510/1971 Babaoff... 346/74 ES 3.673598 6/1972 Simm 346/74 ES 3,715,7622/1973 Magill 346/74 ES FOREIGN PATENTS OR APPLICATIONS 249.786 6/1970U.S.S.R. 346/74 ES Primary E xaminei-Daryl W. Cook AssistantExaminer.lay P. Lucas [57] I ABSTRACT An electrostatic printing systemand method in which a charged particle stream directed toward a print receiving medium is selectively controlled by mechanical and electricalmodulation or shuttering and mechanical motion of the shutter area toachieve character serial and line serial printing.

7 Claims, 37 Drawing Figures PATENTEDJUN 41914 SHEET 30F 6 FIG....7

PATENTEDJun 4 I974 SHEET 5 0f 6 FiG 9 ELECTROSTATIC PRINTING SYSTEM ANDMETHOD USING A MOVING SHUTTER AREA FOR SELECTWE MECHANICAL ANDELECTRICAL CONTROL OF CHARGED PARTHCLES The present invention generallycontemplates pro-- viding a line source of ions for generating an ionstream in the direction of a print-receiving medium which is supportedand transported relative to the ion stream. A printing head isinterposed between the ion source and print-receiving medium whichgenerally blocks the ion stream. The printing head is formed with atleast one shutter area comprising a plurality of electricallyaddressable apertures for electrostatically controlling the flow of ionsthrough the apertures in accordance with electrical signals applied tothe apertures. Thus, while the ion stream is generally mechanicallyblocked by the printing head, ions are selectively passed through theapertures of the shutter area to form on the printreceiving medium, forexample, an electrostatic latent dot matrix which is thereafterdeveloped according to known techniques to provide alphanumericcharacters, images or other symbols. By motion of the printing head theshutter area or shutter areas are transposed in a direction across theprint-receiving medium for selective exposure of ions in accordance withelectrical signals applied to the apertures at sequential positionsacross the print-receiving medium. By this expedient, rows ofelectrostatic latent dot matrices are formed sequentially across theprint-receiving medium for development into, for example, alphanumericcharacters, images and other symbols.

A feature and advantage of the system arrangement using both selectiveelectrical modulation of the ion stream in a shutter area, mechanicalblocking outside the shutter area, and mechanical motion of the shutterarea is that character sequential or character serial and line-by-lineprinting of hard copy alphanumeric output from conventionally codedelectrical signals is achieved for application in data processing anddata transmission systems. Moreover, the character serial and lineserial printing format of the present invention is inherently compatiblewith such applications, thereby eliminating the need for extensive databuffering, affords high printing rates, and permits significantreduction in the complexity of the printer over conventional deviceswith consequent lower costs.

According to one aspect, the invention contemplates effective helicalscanning of a shutter area across a print-receiving medium. In oneembodiment, the printing head which generally blocks the ion stream,supports a shutter area for selectively exposing the printreceivingmedium, and scans the shutter area in a direction across theprint-receiving medium comprises a tube or annular cylinder of solidmaterial surrounding a line source of ions such as a corona wire. Aplurality of aperture groups, each forming a shutter area, are arrangedin a helix around the tubular shutter. Each aperture group includes atleast a row of holes formed through the wall of the tubular shutter andat least one separate conductor is associated with each hole or aperturein an aperture group for electrical addressing of each hole or aperturein a group separate from the other holes in the group. The tube isrotated so that each aperture group or shutter area sequentially arrivesin position for printing or exposing the print-receiving medium withions. Electrical signals are commutated onto the conductors of thetubular shutter for selectively electrically shuttering the apertures ofthe aper ture group in printing position for depositing an electrostaticlatent dot matrix on the print-receiving medium corresponding to aselected alphanumeric character, image or other symbol. The shutter areais, therefore, effectively scanned in line across the printreceivingmedium because of the helical configuration.

In order to prevent ions from passing through other aperture groups inthe helix not in the printing position and thereby contaminating theprint-receiving medium with extraneous electrostatic charges, a printingslot is interposed between the tubular shutter and printreceiving mediumin the form of an ion barrier defining an elongate slot through whichthe ions pass and so'that successive aperture groups in the helix formedon the tubular shutter are brought in sequential alignment with theprinting slot during rotation. The shutter area through which printingis intended at any particular time is sequentially transposed along theprinting slot and across the print-receiving medium. A clockingarrangement is, of course, provided for synchronizing the aperturepositions and the commutated electrical signals. By this uniqueconstruction and arrangement and combination of electrical andmechanical shuttering or modulation, the electrical control apparatus isconsiderably simplified over conventional electrostatic printingequipment. Thus, the number of electrical circuits, electrical drivers,switches and commutators can be significantly reduced. With reference tothe tubular shutter arrangement, only one aperture group is in printingposition at any particular time although a plurality of aperture groupsor shutter areas are provided in the helix around the tube. Thus, asingle conductor can be associated with one hole in each aperture group,row or matrix in the form of a printed metal trace, wire or severalwires. Thus, if each aperture group consists of five apertures or holes,a total of five conductors separately electrically addressed and fiveassociated electrical circuits, drivers and commutators is all thatwould be required for addressing all of the holes of all of the aperturegroups of the tubular printing head. While application of an electricalsignal to one of the conductors addresses a single hole in every one ofthe aperture groups around the helix, only one is in printing position,namely the shutter area aligned with the printing slot, while ionspassing through any other of the aperture groups are mechanicallyblocked. High speed electrical switching of the signals applied to thefive conductors during rotation of the tubular shutter or printing headthus permits high speed character serial and line serial printing aseach shutter area is scanned into position across the print-receivingmedium.

ln a preferred form of the invention, the shutter area comprisesapertures or holes across or through each of which a pair of electricalpotentials is applied to provide double-layered charge or bipolarelectrical control over the aperture. In the example of the tubularshutter, the entire inner surface of the shutter may be coated with alayer of conductive material so that a potential can generally beapplied or maintained on one side of each of the holes or aperturescomprising each of the aperture groups arranged in the helix around thetube. Around the outside of each tube are formed separate conductors forseparately electrically addressing, i.e., applying separate electricalpotentials to each of the holes within an aperture group. These separateconductors may, for example, be in the form of printed metal traces orone or more wires so that a separate electrical potential can be appliedat the outside of each of the holes. A feature and advantage of thisarrangement is that fringing lines of force or electrical fields can beformed and established within the apertures or holes of an aperturegroup between the metal layers or conductors formed on either side ofeach hole for precise control of ions or other charged particlesdirected through the apertures. The orientations and strengths of eachof the fields within the apertures can be controlled by separateelectrical addressing to enhance the flow of ions or other chargedparticles through the holes, block the flow of ions or other chargedparticles through the holes and control the density of flow through thehole over a continuous range in between blocking and enhancing. Thus,the tight electrical control permitted by associating a conductive layeror conductor on either side of each aperture or hole in an aperturegroup permits continuous electrical shuttering control, i.e., 100percent greyscale control over each of the apertures.

According to another aspect of the invention, the printing or exposureof any particular alphanumeric character in the form of an electrostaticlatent dot matrix on the print-receiving medium is itself accomplishedserially or sequentially. Thus, in one form the aperture group orshutter area consists of a row of holes or apertures or two rows ofoffset holes or apertures to provide complete coverage of theprint-receiving medium. As the row of, for example, five holes orapertures is swept across the printing area or printing slot, theelectrical signals applied to the holes for selectively modulating theflow of ions through the holes are switched as the row steps throughsuccessive positions across the printing slot or printing area. Forexample, the electrical signals applied to the separate conductors onone side of the holes can be switched seven times as the row ofapertures or holes comprising the shutter area are swept across theprinting area or printing slot. The result in that case is afive-by-seven dot matrix of dots selectively printed to form the desiredalphanumeric character on the print-receiving medium. Upon completion ofprinting of one dot matrix on the printreceiving medium, the next row ofholes in the helix formed around the tubular shutter arrives in positionand is swept across the printing area or printing slot while theelectrical signals applied to the separate conductors are again switchedseven times to form the next alphanumeric character until a completeline is built up in the character serial mode. The next line is thenprinted by the helix in a line serial mode.

ln order to print a plurality of lines simultaneously on theprint-receiving medium, a plurality of helices each comprisingsuccessive aperture groups can be formed around the tubular shutter,each helix formed with separate conductors for separately electricallyaddressing the holes of the aperture groups in the helix.

In another embodiment of the invention, the printing head is constructedandarranged in the form of an apertured belt rather than a tubular orannular cylinder. The belt is interposed between a line ion source suchas a corona wire and the print-receiving medium which is transportedbeneath the belt and aligned corona wire. The belt generally serves toblock the passage of ions from the corona wire source to theprint-receiving medium except in a shutter area supported by the belt.As heretofore described with reference to the tubular shutter, theshutter area comprises an aperture group or group of holes formedthrough the belt and having a separate electrical conductor associatedwith each of the holes for separate electrical addressing. The belt isarranged across the print-receiving medium and is transported in adirection generally transverse to the direction of transport of theprint-receiving medium so that the shutter area is transposed tosuccessive printing positions across the print-receiving medium. Theangle or orientation between the belt and printreceiving medium can beoffset from the perpendicular to compensate for simultaneous motion ofthe belt and print-receiving medium to provide linear character serialprinting across the print-receiving medium. Electri' cal contacts orbrushes are provided for applying electrical signals to the separateconductors on one side of the belt for separately electricallyaddressing each of the holes in the aperture group or shutter area as itis transposed to successive positions across the printreceiving medium.

In this embodiment, the shutter area or aperture group may consist of acolumn of holes or two columns of offset holes for complete coverageduring printing. The column of holes is transported across theprintreceiving medium and in any particular printing area is sweptacross the printing area while the electrical signals applied to theseparate holes in the columns are switched. if a column of seven holesis provided by way of example and the electrical signals applied to theholes are switched five times in any printing area, a five-by-seven dotmatrix is again provided, the dots in the form of an electrostaticlatent dot matrix on the print-receiving medium which is thereafterdeveloped according to known techniques. Successive dot matricescorresponding to desired alphanumeric characters are thereby formedsequentially across the paper or other printing medium. In order toprovide simultaneous printing of a plurality of lines, a plurality ofbelts can be provided for transporting a plurality of shutter areas oraperture groups across the print-receiving me dium, each separatelyelectrically addressed.

As heretofore described with reference to the tubular shutter, in thepreferred form the belt is formed with a continuous conductive layer onone side of the belt with separate or segmented conductive elements onthe other side of a belt a separate electrical layer or conductorassociated with each of the holes of the aperture group for separateelectrical addressing while a potential is applied to the continuousconductive layer on the other side of the belt. By this expedient, tightelectrical control over the passage of charge particles through theholes can be achieved by means of the fringing lines of force orelectrical fields of selectively controlled orientation and strengthwithin the apertures.

It is apparent that the unique combination of electrical and mechanicalcontrol techniques envisioned by the present invention can beimplemented not only by moving belts and drums but also by discs andother moving elements.

According to yet another aspect of the invention, direct electrostaticprinting onto any print-receiving medium, dielectric or otherwise, canbe accomplished. In this form of the invention, an ion stream iscontrolled by means of a printing head of th type and in the mannersummarized above. However, instead of directly impinging the ion streamon the print-receiving medium which must then be dielectric in order tosupport the electrostatic charge, a liquid aerosol or dry toner cloud isintroduced in the printing slot or printing area between the printingslot and the print-receiving medium so that selectively moduated andshuttered ion stream impinges upon and selectively charges droplets orparticles of the toner cloud which are thereafter accelerated to depositupon the print-receiving medium in accordance with the dot matrixpattern to be reproduced. In this manner, direct toner printing isaccomplished and can be effected upon any printing surface including aconductive surface.

Other objects, features and advantages of the present invention willbecome apparent in the following specification and accompanyingdrawings.

FIG. 1 is a diagrammatic perspective view of a moving apertureelectrostatic printing system for electrically and mechanicallyselectively controlling an ion stream.

FIGS. 2a through 2i are diagrammatic side views of the printing stepsfor printing the electrostatic latent dot matrix of an alphanumericcharacter using the system of FIG. 1.

FIGS. 3a through 3: illustrate the progressive printing of thealphanumeric character corresponding to the steps of FIG. 2.

FIG. 4 is a fragmentary diagrammatic perspective view of the tubularprinting head with shutter areas arranged in a helix.

FIG. 5 is a more complete diagrammatic view of the electrostaticprinting system using a tubular or hollow cylindrical printing headcarrying aperture shutter areas arranged in the helix.

FIG. 5a is a detailed fragmentary plan view of rowaperture shutter areasarranged in the helical configuration.

FIG. Sbis a detailed fragmentary plan view of an alternate two-rowarrangement for the apertured shutter areas arranged in a helix aroundthe tubular printing head.

FIG. 50 is a detailed cross-section of an alternative tubular printinghead helix in which the apertured shutter areas are arranged alonggrooves machined in the surface of the tube.

FIG. 5d, is a plan view of the-machined grooves showing the shutter areaaperture configuration.

FIG. Se is a detailedside cross-section of a groove of the helix showinga conductive wire, an aperture, and lines of force within the aperture.

FIG. 5f is a detailed end cross-section showing a groove of the helix, aconductive wire positioned in the groove and an aperture with the linesof force extending within the aperture.

FIG. 5g is a detailed fragmentary plan view of yet another tubularprinting head helix on a flat surface in which a plurality of conductivewires are associated with each helix of an aperture groove or shutterarea.

FIG. 6 is a side cross-sectional view of a tubular or hollow cylindricalprinting head electrostatic printing I apparatus while FIG. 6a is adetailed fragmentary side cross-section of the tubular or cylindricaldrum printing head showing an aperture shutter area.

FIG. 7 is an end cross-section view of the cylindrical drum printinghead and electrostatic printing appara- IUS.

FIG. 8 is a detailed schematic diagram of the electrical controlcircuitry for the electrostatic printing apparatus of FIGS. 6 and 7.

FIG. 9 is a diagrammatic plan view of an alternative moving apertureelectrostatic printing system for character serial and line serialelectrostatic printing by mechanical and electrical modulation orshuttering of an ion stream using a moving shutter area.

FIG. 10 is a side cross-sectional view of the alternate electrostaticprinting system.

FIG. 11 is a detailed fragmentary plan view of the aperture belt showinga seven aperture column shutter area with a separate electricalconductor for electrically addressing each of the apertures.

FIG. 12 is a diagrammatic perspective view of a moving apertureelectrostatic printing system for direct electrostatic printing on anymedium.

FIG. 13 is a detailed fragmentary side cross-section of a printingaperture for direct electrostatic printing on any medium.

An example of a system embodying the unique combination of electricalmodulation or shutter control over ions moving in an electric field andmechanical motion of the shutter area providing at the same timeeffective mechanical shuttering is shown diagrammatically in FIG. 1. Theion electrostatic printer 10 is adapted for printing, for example, analphanumeric, character in a dot matrix in the form of an electrostaticlatent dot matrix established on dielectric paper 11 which is thereafterdeveloped according to known techniques as, for example, by toning andfixing. The printing apparatus includes a line corona source 12 whichcan be, for example, a row of corona point sources or a corona wire asin the specific example of FIG. 1. A line stream of ions originatingfrom the line corona source 12 is accelerated toward the back electrode13 which may also serve as a support for the dielectric paper or otherdielectric print-receiving medium l l. Interposed between the coronasource 12 and.

print-receiving medium 11 is a printing slit 14 parallel with the coronasource and defined. by a pair of ion barriers 15. Interposed between thecorona source 12 and printing slot 14 and, in fact, circumscribing thecorona source is a tubular shutter 16 in the form of a tube, drum, orannular cylinder formed of at least an insulative layer and a conductivelayer which generally form a barrier to ions originating from the coronasource 12.

In the example of FIG. 1, a row 17 of five apertures 18 is formedthrough the wall of the cylinder or tubularshutter to permit passage ofionsotherwise blocked by as all of the ions are intercepted by the wallof the cylin der. Upon rotation of the cylinder, the row l7of apertures18 moves into the region of the ion flux or stream accelerated towardthe back electrode 13 and also enters the area of printing slit 14 sothat ions may pass through the apertures formed in the wall of thetubular shutter and through the printing slit for establishing theelectrostatic latent dot matrix on the dielectric paper or otherprint-receiving medium 11. By electrically addressing each of theapertures of the row by separate electrical signals commutated onto therotating cylinder, the apertures are electrically turned on or off forelectrically shuttering the ion stream. In writing a character or othersymbol up to five parallel beams of ions are formed by the fiveapertures corresponding to the five horizontal dots of, for example, afive-by-seven dot matrix. As the aperture row or shutter area 17 isswept vertically across the area of the print-receiving medium in theprinting slot, the selected electrical signals applied separately to thefive apertures are switched seven times to form the seven five dot rowsof the character or symbol dot matrix deposited on the dielectric paper1 l. The charge is retained on the dielectric paper or otherprint-receiving medium forming the electrostatic latent dot matrix whichis thereafter developed according to well-known established techniques.

Thus, as the aperture or tubular shutter rotates, the apertures of theshutter area or row 17 move with respect to the paper placing them atsuccessive intervals of time in position to write the successive sevenrows or other number of rows of dots required to form the character dotmatrix. At the successive intervals of time corresponding to thesuccessive row positions, the apertures are electrically addressed orswitched according to selected electrical signals for passing orblocking the ion stream or controlling the ion stream over a continuousrange in between, providing effectively infinite grey-scale control ashereinafter more fully described.

The hollow cylinder or tubular shutter 16 which forms the moving elementof the electro-mechanical shutter is also referred to herein as theprinting head and can assume a variety of configurations.

FIGS. 2a through 2i illustrate diagrammatically the steps in thesequential printing of an alphanumeric character or other symbol, inthis example the capital letter A, using the simple apparatus of FIG. 1.As the tubular shutter rotates sweeping the row of apertures across theprinting slot, the selected electrical signals applied to each of theapertures is switched at successive intervals of time corresponding inthis example to the seven row positions of the five-by-seven dot matrix.At each of the successive seven time intervals corresponding to theseven row positions, the apertures of the row selectively pass or blockions according to the applied signals depositing the electrostaticlatent dot matrix in the desired configuration on the printreceivingmedium. The results of the printing at each of the steps illustrated inFIGS. 2a through 21' is shown in the corresponding FIGS. 3a through 31'.

In order to achieve character serial printing repeated in a line-by-linefashion as the paper is advanced, the shutter area must be transposedacross the paper. This is accomplished in the example illustrateddiagrammatically in FIG. 4 by arranging a plurality of shutter areaseach in the form of a row of apertures in a helical configuration aroundthe tubular shutter. As heretofore described with reference to FIG. 1,the elongate, hollow cylinder or drum 20 circumscribes a corona wire 21which provides the line source of ions accelerated in the direction of aback electrode 22 which may serve as the support for a dielectric paperor other printreceiving medium 23. The printing slot 24 parallel withthe line ion source 21 and defined by ion barriers 25 is interposed inthe ion stream between the tubular shutter 20 and print-receiving medium23. A plurality of shutter areas 26 through 31, etc. are arranged in ahelical configuration around the cylinder 20. Each shutter area is inthe form of a row of apertures 32 formed through the cylinder wall andspaced laterally with respect to each other in accordance with thedesired spacing between alphanumeric characters or other symbols to beformed on the paper. By selecting a cylinder or tubular shutter 20 longenough to cover an entire printing line and locating each of theaperture rows or shutter areas 26 through 31, etc. at suitable intervalsalong the helix, the shutter areas will enter the printing slit region24 successively one after another and viewed through the slit willappear to move laterally across the print-receiving medium until anentire line of characters or other symbols has been established. Thus,the single rotational motion of the drum provides both the vertical scanfor establishing and printing each individual character dot matrix andalso provides the apparent lateral motion of the shutter area across thepaper as required for successive or character serial printing in ahorizontal line simulating typewriter action.

The paper is advanced for printing successive lines in the same mannerand simultaneous multiple line printing in the character serial mode ispossible by providing a number of helices around the tubular shutter ina number equal to the lines to be printed. The shutter areas in eachhelix are of course separately electrically controlled.

A feature and advantage of the helical arrangement is that while it ispossible to'drive each of the holes or apertures formed in the helicalrow independently, in fact only five electrical drivers or switches arenecessary for electrically addressing all of theapertures in the shutterareas arranged in the helical configuration around the tube. Thus, eachaperture is electrically connected to a corresponding aperture in eachof the shutter areas. While each of the apertures in a particularshutter area is separately electrically addressable, all of the shutterareas are thereby addressed simultaneously. Only one of the shutterareas, however, is in the printing position over printing slot 24 at anyparticular time.

A variety of tubular shutter structures for accomplishing separateelectrical addressing of the apertures in a particular shutter areawhile simultaneously addressing all of the shutter areas are illustratedby way of example in FIGS. 5a through 5g. By these arrangements, aconsiderable simplification in the electrical circuitry and structureover conventional electrostatic matrix head printers is achieved. Asshown in FIG. 5, the moving printing head is a tubular shutter 40 of thetype illustrated in FIG. 4 formed of a central insulating layer 41 ofplastic tubing or similar material coated on its inner surface with aconductive metal layer 42. Around the outside of the tubular shutter 40are supported the separate or segmented conductors for separatelyelectrically addressing the apertures of shutter areas arranged in thehelix 43 around the cylinder. The cylinder 40 is mounted on shaft 44which forms the axis around which the cylinder is rotated and which alsoprovides the support for a line ion source such as a corona wire mountedwithin the cylinder. Mounted on the shaft 44 which is fixed to androtates with the rotating tubular shutter 40 is the electrical signaltransfer assembly 45 consisting of, for example, conductive bandsoperating in association with brushes for commutating electrical signalsonto the cylinders. The conductive bands 46 are electrically coupledwith the separate conductors arranged around the outside of the cylinderas hereinafter described in detail for separate electrical addressing ofthe apertures of the shutter areas. Synchronization of the selectedelectrical addressing signals and the position of the successive shutterareas with reference to a printing slot is accomplished by means of thetiming'wheel disc 47 which is fixed for rotation on the shaft 44. Thetiming disc may utilize, for example, either photo-optical or electricalpick-up for controlling the application of electrical signals to thecommutating brush and band assembly according to the position of thecylinder or drum. For example, as each new shutter area, which in thecase of FIG. a is a five aperture row, enters the printing region orarea of the printing slot, the timing disc 47 provides a timing signalindicating the start of the next character or symbol to be printed andalso the end of a particular line. Because the timing wheel or discassembly 47 is rigidly fixed with respect to the cylinder or drum 40,the drum rotation speed and stability is not critical.

Referring to FIG. 5a, one structural arrangement for the separateconductors formed on the outside of the cylinder or drum 40 is shown. Inthis example, the drum is formed with a smooth outer surface with fivemetal strips or traces 48 formed in a helix around the drum coincidingwith the helical configuration of the successive shutter areas oraperture groups. Each of the five metal strips or traces printed,deposited or otherwise formed around the plastic tubular support of drum'40. is electrically or insulatively isolated from every other strip.Each of the strips 48 also provides a conductive layer around anaperture in each of the successive shutter areas. In the example of FIG.50, each of the successive shutter areas comprises a single row of fiveapertures laterally and vertically displaced from the aperture row oneither side. In this geometrical configuration, a single metal strip 48surrounds and electrically connects the correspondingly positioned holein each of the aperture rows of shutter areas. Thus, one of the metalstrips or traces 48 electrically connects each of the left-mostapertures 50 of each aperture row or shutter row. A second strip ortrace 48 surrounds and electrically connected the aperture next to theleft-most aperture of each aperture row or shutter area, etc.

Another shutter area configuration is illustrated in FIG. 5b. Accordingto this arrangement, each shutter area is formed not by a single row offive holes or apertures but by a pair of rows, one row 51 of two holesand the other row 52 of three holes offset with reference to each otherto provide complete coverage during printing. Thus, each of theapertures in the offset rows of two and three holes are separatelycontrolled electrically by metal strips 53 to print a single row of fivedots. However, because of the overlap of the printing apertures theformed dots will also overlap to form a solid line.

In the configuration of FIGS. 50 and 5d, a set of, for example, five.grooves 54 are machined in a helical array around the plastic tube 41coinciding with the helical configuration of the shutter areas. Holesare drilled in the valleys of the grooves at successive intervals aroundthe helix to form the aperture groups or shutter areas. As describedwith reference to FIGS. 5a and 5b, the holes can be formed in theconfiguration of a single row of five apertures or in the configurationof a pair of two offset rows.

Referring in more detail to FIGS. 5c and 5d, a conductive wire 55 isseated at the base of each groove 54 so that a wire 55 overlies a holein each aperture group formed in the grooves 54 for separate electricaladdressing of each hole in an aperture group.

As shown in the side eross-section and end crosssection of FIGS. 5e and5f respectively each of the holes or apertures 58 is formed through theplastic tube 60 which provides the structural support for the tubular orhollow cylindrical printing head. The tube may be formed however of anyinsulative material. As heretofore described the inside surface ofthetube or drum is coated with a layer 61 of conductive material, sothat a conductor is formed on either side of each of apertures 58. Themetal or other conductive layer 61 constitutes a continuous conductivelayer to which a selected fixed potential is supplied therebyestablishing a fixed potential at one opening or side of each of theapertures 58. At the outside surface of the drum or hollow cylinderhowever the conductive wires 55 effectively provide a segmentedconductive layer of insulatively isolated segments for establishingseparate or different selected potentials at the other opening or sideof each of the apertures 58 of an aperture group. The result is thatlines of force are established between the conductive wires 55 on oneside of the apertures and the continuous conductive layer 61 on theother side.

A critical feature and advantage of this arrangement is that lines offorce or fringing fields are established within the apertures forprecisely controlling the flow of charged particles directed through theapertures of the shutter area. The strength or magnitude and orientationof the fringing fields established within the apertures is controlledselectively by the signals or potentials applied to the separateconductors 55 which separately address one side of each of the aperturesin each of the aperture group and the common potential applied to thecontinuous conductive layer 61 formed on the inner surface of the tubeor cylinder.

Similarly with respect to the embodiment described with reference toFIG. 5a the separate selected electrical potentials are applied to theinsulatively isolated metal strips or hands 48 while the commonelectrical potential is applied to the continuous conductive layer 42coated on the inner surface of the cylinder. Again by this expedientfringing fields of force are established within the apertures of theaperture group or shutter area of controlled strength or magnitude andorientation according to the applied potentials. In this respect theinvention incorporates principles described in US. Pat. Application Ser.No. 864,022 entitled Electrostatic Line Printer, assigned to the commonassignee of the present case. The Electrostatic Line Printer inventionset forth in that case incorporates a multi-layered particle modulatorin one embodiment formed by a layer of insulating material having acontinuous layer of conducting material formed on one side of theinsulating layer and a segmented layer of conducting material formed onthe other side of the insulating layer. At least one row of apertures isprovided through the multilayered particle modulator and each apertureis substantially surrounded byor associated with a segment of thesegmented layer of conductive material. Each segment of the segmentedlayer is insulatively isolated from every other segment for separateelectrical control and addressing of each of the apertures. By means ofthe multiple layer configuration, selective potentials applied to thesegments of the segmented conductive layer, while a fixed potential isapplied to the continuous conductive layer, results in a double layer ofcharges selectively establishing fringing fields within the apertures ofthe modulator. The modulator is interposed in an overall appliedaccelerating electrostatic field which projects charged particlesthrough the row of apertures of the particle modulator. The crosssectional flow density of the particle stream is regulated by thefringing fields which are contained within the apertures and isprecisely controlled according to the pattern of potentials applied tothe segments of the segmented conductive layer. By this means, enhancingfields, blocking fields and fields of a continuous range of magnitudebetween blocking and enhancing can be established within the aperture ofthe modulator for controlling the flow of particles through theapertures over a continuous grey-scale range.

These features of the Electrostatic Line Printer described in thatpatent application Ser. No. 864,022 are achieved in the moving printinghead of the electrostatic printing system of the present invention bythe arrangement of conductors on either side of the openings of theapertures of each aperture group, separately electrically addressable onat least one side'for selectively electrically addressing the aperturesof each group.

Yet another aperture group construction arrangement for the hollowcylindrical printing head of 55 is illustrated in FIG. g. In thisembodiment the tube is formed with a smooth outer surface and aplurality of wires 63 in this case 3 in number are associated with eachaperture 64 of an aperture group for more complete electrical controlover the outer opening of the aperture 64. In this arrangement the threewires 63 seated on one side of the aperture 64 can be simultaneouslyaddressed by the same potential signal or different potentials can beapplied for achieving desired printing effects.

The electro-mechanical apparatus for an electrostatic printer of thetype described with reference to FIG. 5 is illustrated in FIGS. 6through 8. Referring to FIGS. 6 and 7 the tubular or hollow cylindricalprinting head is mounted on a base 70 and side support 71 which supportthe axes 72 and 73 on which the printing drum 74 is mounted forrotation. The axis 72 is fixed to the drum 74 and rotates with the drumwithin bearings 81 and bearing 82. The axis 73, on the other hand isfixed with reference to the base 70 and side support 71 and the drum 74rotates relative to the axis 73 around bearings 83. The drum 74 isformed with a hollow cylindrical or tubular side wall 75 through whichthe printing apertures are formed with the aperture groups orshutter-areas arranged in a helix around the wall 75 of the drum asheretofore described. Mounted inside the drum 74 and the drum wall 75 isthe corona wire support mount 77 which is fixed to the stationary axis73 thereby supporting the corona wire 78 adjacent the wall 75 of thecylinder but at a position stationary relative to the rotating drum. Thecorona wire mounting structure 77 is supported at its opposite end bythe innerend of axis 72 which rotates inside a brushing 84 relative tothe corona wire support.

An ion stream originating from corona wire is accelerated in thedirection of a back electrode which forms a cover over the paper 85 orother printreceiving medium. Ions of the stream that are selectivelypassed through apertures in the wall 75 of drum 74 pass through aprinting slot 86 to be deposited on the paper or other print-receivingmedium 85. Paper is fed across the upper surface of the printing slotbetween the printing slot 86 and back electrode 80 by means of a rotarysolenoid 87 which advances the paper one character line at a time aftera complete line has been printing by driving rollers 88.

Electrical addressing of the separate electrical conductive strips orwires formed in the helical configuration around the outer surface ofthe wall 75 of drum 74 .is accomplished by means of slip rings 90 formedon disc 91 mounted on support 92 which provides the drive pulley for thedrum. Thus the disc 91 and drive pulley 92 are fixed to the rotatingshaft 72 for rotation with the drum. Electrical signals are applied tothe rings 90 of the disc 91 by means of brushes 93. As shown in FIG. 6the set of brushes 93 includes four brushes which maintain electricalcontact with four of the seven slip rings of disc 91. A second set ofbrushes containing three brushes for maintaining electrical contact withthe other three slip rings of the set of seven slip rings formed on disc91 is at a position 90 from the set of brushes 93 and is not visible inthe cross-section of FIG. 6 Electrical signals fed through the brushes93 and slip rings 90 are connected via a set of wires 95 to the set ofseparate conductors formed along the outer surface of the wall 75 ofdrum 74, to the continuous conductive layer formed around the innersurface of wall 75 of the drum, and for printing control. Thus, of theseven leads from the slip ring, five provide separate electricaladdressing for the five separate conductors either wires or metal stripsformed in a helix around the outer wall 75 of the drum 74. In thisexample each aperture group comprises five apertures separatelyelectrically addressable by the five leads. The sixth electrical lead iselectrically connected to the metal layer formed around the innersurface of the wall 75 of drum 74 for applying a selective fixedpotential to the inner metal layer. Finally the seventh lead provides aprinting control signal hereinafter described.

The control electronics for the printing apparatus of FIGS. 6 and 7 isshown in FIG. 8 and centers around the character generator whichgenerates the five electrical control signals applied to the fiveseparate conductors formed around the outer surface of the drum. Thefive outputs of character generator 100 control the gates of fivetransistors 101 which in turn provide the five signal outputs appliedthrough brushes and slip rings to the separate conductors formed aroundthe outer surface of the drum. The five output signals 102 selectivelycontrol the magnitude and orientation of the fringing fields within theapertures of an aperture group or shutter area selectively turning theholes on and off and adjusting them over a continuous grey-scale range.

Seven input switches 103 to the character generator 100 control the fiveaperture control signals, the signal potential applied to the conductivelayer of the inner surface of the drum and a seventh printing controlsignal. The three inputs 104 to character generator 100 provide rowcontrol during printing of a particular dot matrix constituting forexample an alphanumeric character. Thus, in the case of a five by sevendot matrix, five dots or holes are addressed in seven rows theelectrical signals applied to the apertures changing with each of theseven rows of the dot matrix. The inputs 104 provide the row control forprinting the seven separate rows of the five by seven dot matrix. Thesignal on line 105 provides an indication that the particular dot matrixis completed. The row address signals for printing the rows of aparticular dot matrix are generated by the divide-by-l6 counters 106 and107 and associated logic circuitry which provide a count down of clockfrequencies generated by the oscillator or clock 108 which is, forexample, a multi-vibrator. The timing pulses to initiate characterprinting originates from photo-electric pick-up 110 via gate 111. Thistiming pulse also resets the character generator.

Monostable multi-vibrator 112 in association with the signal fromphoto-electric pick-up 110 provides the reference pulse from gate 111which indicates a zero point for initiating printing of a characterline. Flip-flop 113 provides an indication pulse after one revolution ofthe drum indicating completion of printing of a charac ter line. A onerevolution indicator pulse from flip-flop 113 in turn controls flip-flop114 alternatively turning the clock 108 and advance paper pulse on andoff. Thus, during one revolution or rotation of the drum the clock 108is on, generating signals for printing a row or line of characters.Flip-flop 114 then shuts off clock 108 and during the second rotation ofthe drum or cylindrical printing head actuates the advanced paper pulsefor advancing the paper or other print-receiving medium one characterline during the period of the second rotation. During alternaterotations of the drum a line is printed and the paper advanced as theclock is turned on during one rotation and then turned off during thenext rotation while an advanced paper pulse is generated. The advancedpaper pulse actuates rotary solenoid 87 which by means of rollers 88advances the paper 85 or other print-receiving medium one characterline.

An alternative structure and arrangement for a moving aperture ioncontrolled electrostatic printer is illustrated in FIGS. 9 through 11.In this arrangement the moving printing head which provides bothelectrical and mechanical shuttering of the generated ion streem is inthe form of a moving belt 200 arranged for movement and transport acrossthe paper or other printreceiving medium 201. The belt 200 physicallyblocks the passage of ions originating from corona source 202 travellingin the direction of a back electrode not shown. The corona wire issuspended between two supports 203 and 204 mounted stationary relativeto the moving belt and which support the corona wire in a directionparallel and over the elongate belt. The belt 200 is driven by means ofmotor 205 between rollers or pulleys 206 and 207 by means of gear box208. The motor 205 also drives a paper strip 210 from a paper supplyroll 211 to a developer assembly 212 which may be for example a towerbath assembly which develops the latent electrostatic dot matricesestablished on the paper or other print-receiving medium.

The belt 200 is formed with a set of apertures or holes therethroughwhich constitute the aperture group or shutter area which is transportedfrom one side of the tape 201 to the other side between rollers 206 and207. The roller 206 is driven by motor 205 while roller 207 is mountedas an idler pulley with tension adjustment assembly 213. As shown inFIG. 10 the belt 200 is in the form of an endless belt mounted aroundthe pulleys 206 and 207. A fragmentary segment of the belt is shown inFIG. 11 in which a single aperture group or shutter area 220 is formedthrough the belt consisting of a column of seven holes 221. The aperturegroup 220 consisting of a column of seven holes is transportedhorizontally across the paper as motor 205 drives the endless beltaround pulleys 206 and 207 for printing of electrostatic latent dotmatrices at successive character positions. The ions are blockedphysically from reaching the paper everywhere except at the aperturecolumn group or shutter area 220.

The belt is formed of an insulative strip or carrier 222 coated on theinner surface with a layer 223 of metal or other conductive material. Onthe outside of the insulative belt layer 222 are formed a plurality ofseparate conductive strips 224 of metal or other conductive material forseparately electrically addressing the apertures 221. Thus, sevenconductive strips 224 are provided each insulatively isolated from everyother strip and each substantially surrounding one of the apertures 22]of the shutter area.

As heretofore described separate selected electric signals are appliedto the conductive strips 224 while a selected fixed potential is appliedto the continuous conductive layer 223 on the underside of the belt sothat a double layer charge is established at each aperture with onepotential at one side or opening of the aperture and another potentialestablished at the other side or opening of the aperture. The potentialsignals are selected to establish within the apertures fringing fieldsof force of selected strength or magnitude and orientation for controlof ion flow through the apertures.

Electrical signals are applied to the conductive segmented strips 224 byway of an electrical contact pulley 225 which maintains electricalcontact with the separate electrically conductive strips formed on thebelt 220 as it passes around roller or pulley 206. Thus while motor 205drives the roller 206, electrical contact pulley 225 in frictionalengagement with roller 206 is also driven in turn rotating the slip ringassembly 226 to which suitable electrical brushes are applied. Separateelectrical signals for addressing the conductive strips 224 can bederived from an electrical control assembly of the type illustrated inFIG. 8 but with seven outputs from the character generator forapplication to the seven conductive strips.

During printing of an alphanumeric character or other symbol or imagethe embodiment of FIGS. 9 through 11 can be operated in a five-by-sevendot matrix mode. Thus, the seven columns would be successively switchedand addressed at five column positions for a particular character orsymbol as the column is swept through five successive column positionsby movement of the belt. Successive five-by-seven dot matrix charactersare thereby printed across the printreceiving medium or paper 201 untila full line is completed. The printer can thereby be operated in acharacter serial and line serial mode.

During printing the belt 200 can be oriented in a directionperpendicular to the paper or printing medium with the paper steppedintermittently for line-by-line printing. However, in the example ofFIG. 9 the paper 201 is transported continuously from paper supply roll211 to the developer assembly 212 while the belt 200 is continuouslydriven across the paper. Therefore the belt is oriented at an angle withrespect to the paper to compensate for paper motion and continuouscharacter serial and line serial printing is achieved.

Additionally a plurality of aperture groups can be provided on a singlebelt or a plurality of belts can be provided for printing more than oneline and more than one section of a line at a time. 7

It is apparent that other moving printing head configurations can beconstructed to embody the moving printing head for both electrical andmechanical shuttering of an ion stream such as a variety of drum, disc,and belt arrangements. Thus, yet another embodiment the line ion sourceis arranged in the configuration of a circle and the movable apertureprinting head comprises a disc carrying a shutter area in the form of arow or column of apertures formed through the disc. The disc isinterposed between a line ion source which is arranged in a circle and aprint-receiving medium to block the stream of ions originating from theion source except in the shutter area. Separate electrical conductorsare provided on the surface of the disc for separately electricallyaddressing the apertures of the shutter area in turn selectively tocontrol the passage of ions through the aperture area. The aperture areais transposed in a circular mode by rotation of the disc for printingthe sequential positions of the print-receiving medium.

A moving aperture electrostatic printing system for printing on anysurface or print-receiving medium including conductive materials isillustrated in FIGS. 12 and 13. In the embodiment illustrated thereinthe moving printing head consists of a rotating tubular cylinder or drum300 of the type heretofore described. A rotataing drum or cylinder isformed by a central insulative layer 301 which may be for example aplastic tubing coated on its inner surface by a continuous conductivelayer 302 of metal or other conductive material. An array of aperturegroups forming the shutter areas is arranged in a helical configurationaround the tube with a segmented conductive layer 303 formed by separatemetal strips or wires formed on the outer surface of the tube forseparately electrically addressing each of the holes or apertures ofeach aperture group. A corona wire source 304 suspended within thetubular printing head 300 provides a stream of ions directed toward backelectrode 305 and the print receiving medium 306 which may be made ofany material suitable for receiving toner particles including bothconductive and dielectric material. Instead of a single printing slotinterposed between the printing head 300 and printreceiving medium 306as in the embodiment heretofore described, a pair of printing slotsformed by a first pair of barriers 307 and a second pair of barriers 308is interposed in the ion stream path between the printing head 300 andprint-receiving medium 306. The two pairs of barriers 307 and 308 definea channel or passageway 310 through which toner particles are deliveredin the direction of arrow 3] I.

As shown in more detail in FIG. 13 uncharged toner particles 312generated by a suitable toner source 313 are transferred through thechannel 310 and across the printing slot formed by the two pairs ofbarriers 307 and 308 to encounter a stream of ions 313 originating fromcorona wire 304 and accelerated in the direction of back electrode 305.The toner particles 312 may be in the form of dry toner particles orliquid aerosol droplets and the toner source 313 provides a cloud whichis carried by a suitable air pressure differential through the channel310 and across the printing slot and stream of ions 313.

The stream of ions 313 is intercepted by the wall of the tubularprinting head 300 and is thereby blocked except in the location ofapertures 314 of an aperture group which have been separatelyelectrically addressed along the separate conductive strips or wires 303to permit passage of ions 313 through the apertures 314. The fringingelectrical fields of force within the apertures 314 extending betweenconductive layers 302 and 303 can be established at selectedorientations and strengths according to the potential applied to theconductive layer 302 and according to the selected potentials applied tothe separate conductive strips or wires 303 addressing the apertures314.

Ions 313 selectively passed through particular apertures 314 in anaperture group encounter and impinge upon the uncharged toner particles312 delivered through channel 310 selectively charging the particleswhich are thereafter accelerated toward the back electrode 305depositing upon the print-receiving medium 306 for direct toner markingprinting. Thus, the initially uncharged toner particles 312 deliveredbetween the printing head 300 and print-receiving medium 306 areselectively charged by the selectively passed ion stream to beaccelerated and deposited upon the print receiving medium 306 inaccordance with the pattern or image to be reproduced. The depositedtoner marking particles can thereafter be fixed according to knowntechniques.

Other arrangements and configurations of system for direct toner markingon any material applicable in the present invention are set forth inUnited States Patent Application Ser. No. l0l,68l entitled ElectrostaticPrinting System and Method Using Ions and Toner Particles, assigned tothe assignee of the present case.

What we claim is:

1. An electrostatic printer comprising:

means for transporting a print receiving medium;

means for generating a line source of ions in the direction of saidprintreceiving medium;

means for blocking the ion stream, for providing a shutter area forselectively exposing the printreceiving medium, and for sequentiallyscanning the shutter area in a direction across the printreceivingmedium comprising a tubular shutter of solid material surrounding theline source of ions and having a plurality of aperture groups arrangedin a helix around said tubular shutter, each aperture group comprisingat least a row of holes formed through the wall of the tubular shutter,each hole in a row having at least one conductive element associatedwith said hole separate from the conductive element associated with eachother hole in the row;

means for rotating said tubular shutter;

means for selectively electrically shuttering the apertures in each rowcomprising means for commutating'electrical signals on to the conductorsassociated with apertures in said tubular shutter;

and a printing slot interposed between the tubular shutter and printreceiving medium comprising an ion barrier defining an elongate slotwhereby suceessive aperture groups in the helix formed on said tubularshutter are brought in sequential alignment with said printing slotduring rotation of the tubular shutter so that a shutter area issequentially transposed along the printing slot and across theprintreceiving medium.

2. An electrostatic "printer set forth in claim 1 wherein said tubularshutter comprises a cylindrical tube of non-conductive material havingcoated over the inner surface thereof a continuous layer of conductivematerial, and having formed on the outer surface thereof a plurality ofconductive elements at least one conductive element associated with eachhole of an aperture group.

3. An electrostatic printer comprising:

means for transporting a print receiving medium;

means for generating a line source of ions in the direction of saidprint-receiving medium;

means for blocking the ion stream, for providing a shutter area forselectively exposing the printreceiving medium, and for sequentiallyscanning the shutter area in a direction across the print receivingmedium comprising a belt aligned between the line source of ions and theprintreceiving medium said belt formed with a shutter area of a group ofapertures comprising at least a column of holes formed through the belteach hole in the column having at least one conductive elem'entassociated with said hole separate from the conductive elementassociated with each other hole in said column;

means for transporting said belt across the printreceiving medium;

and means for selectively electrically shuttering the apertures in thecolumn formed through said belt comprising means for commutatingelectrical signals onto the conducting elements associated with theapertures in said belt.

4. A method of electrostatic printing comprising:

supporting and transporting a print-receiving medium;

directing a line stream of ions toward the printreceiving medium;

interposing a printing slot in the stream of ions;

blocking the line stream of ions in the printing slot with an ionbarrier;

providing a shutter area of a row of electrical addressable apertures inthe line stream of ions;

selectively applying electrical signals to the electrically addressableapertures of the shutter area selectively and electrically to shutterions directed through the printing slot;

sweeping the row of apertures across the printing slot while switchingthe electrical signals applied to the apertures;

and transposing the shutter area sequentially along the printing slotfor selectively exposing the printreceiving medium to ions at sequentialpositions across the print-receiving medium.

5. An electrostatic printer comprising:

a tubular printing head formed with a plurality of aperture groupsarranged in the configuration of a helix around said tubular printinghead, each aperture group comprising a shutter area, at least oneconductor associated with each aperture, said apertures formed throughthe wall of said tubular printing head;

means for supporting and transporting a print receiving medium past aposition adjacent said tubular printing head;

back electrode means located on one side of the print receiving mediumposition opposite said tubular printing head;

a line source of ions arranged within said tubular printing head fordirecting an ion stream toward the back electrode means;

means for rotating said tubular printing head;

ion barrier means defining a printing slot interposed between saidtubular printing head and said print receiving medium position whereby,upon rotation of said tubular printing head, the shutter area iseffectively transposed across the printing slot and print receivingmedium position while each aperture group is swept across the printingslot in a direction generally orthogonal to the direction of thetransposition of the shutter area;

means for selectively applying electrical signals to the conductorsassociated with said apertures to electrically selectively shutter ionsthrough said apertures in the shutter area;

means for synchronizing the shutter area position and said electricalsignals.

6. An electrostatic printer comprising:

means for supporting and transporting a print receiving medium past aposition;

back electrode means located on one side of said print receiving mediumposition;

a line source of ions arranged along the other side of said printreceiving medium position for directing an ion stream toward the backelectrode means;

belt means for blocking the ion stream originating at said line sourceof ions, for providing a shutter area for selectively passing ions fromthe ion stream, and for transposing the shutter areas sequentially alongsaid line source of ions, said shutter area comprising a plurality ofsaid apertures formed through said belt means, said shutter area interposed between said line source of ions and said print receiving mediumposition, said belt means comprising a layer of non-conductive materialhaving coated on one side thereof a continuous layer of conductiblematerial, and having formed on the other side thereof a plurality ofconductive elements, at least one conductive element associated witheach hole of the aperture group;

means for sweeping said shutter area in a direction generally orthogonalto the direction of transposition of said shutter area;

means for applying electrical signals to the holes of said shutter areaand for switching said electrical signals during the sweeping of theaperture group orthogonally to the direction of transposition of theshutter area to electrically selectively shutter ions through saidapertures in the shutter area; and

means for synchronizing the shutter area position and said electricalsignals.

7. An electrostatic printer as set forth in claim 6 wherein is providedmeans for switching the electrical signals supplied to the separateconductive elements of each aperture of an aperture group duringrotation of said aperture group across a printing slot whereby a latentelectrostatic dot matrix is formed on said printreeeiving medium by eachaperture group.

1. An electrostatic printer comprising: means for transporting a printreceiving medium; means for generating a line source of ions in thedirection of said print-receiving medium; means for blocking the ionstream, for providing a shutter area for selectively exposing theprint-receiving medium, and for sequentially scanning the shutter areain a direction across the print-receiving medium comprising a tubularshutter of solid material surrounding the line source of ions and havinga plurality of aperture groups arranged in a helix around said tubularshutter, each aperture group comprising at least a row of holes formedthrough the wall of the tubular shutter, each hole in a row having atleast one conductive element associated with said hole separate from theconductive element associated with each other hole in the row; means forrotating said tubular shutter; means for selectively electricallyshuttering the apertures in each row comprising means for commutatingelectrical signals on to the conductors associated with apertures insaid tubular shutter; and a printing slot interposed between the tubularshutter and print receiving medium comprising an ion barrier defining anelongate slot whereby successive aperture groups in the helix formed onsaid tubular shutter are brought in sequential alignment with saidprinting slot during rotation of the tubular shutter so that a shutterarea is sequentially transposed along the printing slot and across theprintreceiving medium.
 2. An electrostatic printer set forth in claim 1wherein said tubular shutter comprises a cylindrical tube ofnon-conductive material having coated over the inner surface thereof acontinuous layer of conductive material, and having formed on the outersurface thereof a plurality of conductive elements at least oneconductive element associated with each hole of an aperture group.
 3. Anelectrostatic printer comprising: means for transporting a printreceiving medium; means for generating a line source of ions in thedirection of said print-receiving medium; means for blocking the ionstream, for providing a shutter area for selectively exposing theprint-receiving medium, and for sequentially scanning the shutter areain a direction across the print-receiving medium comprising a beltaligned between the line source of ions and the print-receiving mediumsaid belt formed with a shutter area of a group of apertures comprisingat least a column of holes formed through the belt each hole in thecolumn having at least one conductive element associated with said holeseparate from the conductive element associated with each other hole insaid column; means for transporting said belt across the print-receivingmedium; and means for selectively electrically shuttering the aperturesin the column formed through said belt comprising means for commutatingelectrical signals onto the conducting elements associated with theapertures in said belt.
 4. A method of electrostatic printingcomprising: supporting and transporting a print-receiving medium;directing a line stream of ions toward the print-receiving medium;interposing a printing slot in the stream of ions; blocking the linestream of ions in the printing slot with an ion barrier; providing ashutter area of a row of electrical addressable apertures in the linestream of ions; selectively applying electrical signals to theelectrically addressable apertures of the shutter area selectively andelectrically to shutter ions directed through the printing slot;sweeping the row of apertures across the printing slot while switchingthe electrical signals applied to the apertures; and transposing theshutter area sequentially along the printing slot for selectivelyexposing the print-receiving medium to ions at sequential positionsacross tHe print-receiving medium.
 5. An electrostatic printercomprising: a tubular printing head formed with a plurality of aperturegroups arranged in the configuration of a helix around said tubularprinting head, each aperture group comprising a shutter area, at leastone conductor associated with each aperture, said apertures formedthrough the wall of said tubular printing head; means for supporting andtransporting a print receiving medium past a position adjacent saidtubular printing head; back electrode means located on one side of theprint receiving medium position opposite said tubular printing head; aline source of ions arranged within said tubular printing head fordirecting an ion stream toward the back electrode means; means forrotating said tubular printing head; ion barrier means defining aprinting slot interposed between said tubular printing head and saidprint receiving medium position whereby, upon rotation of said tubularprinting head, the shutter area is effectively transposed across theprinting slot and print receiving medium position while each aperturegroup is swept across the printing slot in a direction generallyorthogonal to the direction of the transposition of the shutter area;means for selectively applying electrical signals to the conductorsassociated with said apertures to electrically selectively shutter ionsthrough said apertures in the shutter area; means for synchronizing theshutter area position and said electrical signals.
 6. An electrostaticprinter comprising: means for supporting and transporting a printreceiving medium past a position; back electrode means located on oneside of said print receiving medium position; a line source of ionsarranged along the other side of said print receiving medium positionfor directing an ion stream toward the back electrode means; belt meansfor blocking the ion stream originating at said line source of ions, forproviding a shutter area for selectively passing ions from the ionstream, and for transposing the shutter areas sequentially along saidline source of ions, said shutter area comprising a plurality of saidapertures formed through said belt means, said shutter area interposedbetween said line source of ions and said print receiving mediumposition, said belt means comprising a layer of non-conductive materialhaving coated on one side thereof a continuous layer of conductiblematerial, and having formed on the other side thereof a plurality ofconductive elements, at least one conductive element associated witheach hole of the aperture group; means for sweeping said shutter area ina direction generally orthogonal to the direction of transposition ofsaid shutter area; means for applying electrical signals to the holes ofsaid shutter area and for switching said electrical signals during thesweeping of the aperture group orthogonally to the direction oftransposition of the shutter area to electrically selectively shutterions through said apertures in the shutter area; and means forsynchronizing the shutter area position and said electrical signals. 7.An electrostatic printer as set forth in claim 6 wherein is providedmeans for switching the electrical signals supplied to the separateconductive elements of each aperture of an aperture group duringrotation of said aperture group across a printing slot whereby a latentelectrostatic dot matrix is formed on said print-receiving medium byeach aperture group.